In a manufacturing process of a semiconductor device or a liquid crystal display, a plasma processing apparatus such as a plasma etching apparatus, a plasma CVD film forming apparatus, or the like is used to perform a plasma process such as an etching process, a film forming process, or the like on a target substrate to be processed such as a semiconductor wafer, a glass substrate, or the like.
Recently, for the plasma processing apparatus, some attention has been paid to an RLSA™ microwave plasma processing apparatus capable of uniformly generating a high density plasma having a low electron temperature (see, e.g., Japanese Patent Application Publication No. 2007-109457).
The RLSA™ microwave plasma processing apparatus includes a planar antenna (a radial line slot antenna) provided above a chamber, the planar antenna having a plurality of slots formed in a predetermined pattern. Microwaves from a microwave generating source are radiated through the slots of the planar antenna into a vacuum-sealed chamber via a microwave transmitting plate made of a dielectric. A thus-generated microwave electric field turns a gas, introduced into the chamber, into a plasma, by which a plasma process is performed on a target substrate such as a semi-conductor wafer or the like.
In addition, there has been proposed a microwave plasma processing apparatus including a microwave plasma source in which a plurality of microwaves is distributed and guided into a chamber via a plurality of antenna modules having the planar antenna, and the microwaves are spatially combined in the chamber (see, e.g., International Patent Publication No. 2008/013112).
In such a type of microwave plasma processing apparatus, an impedance matching unit (tuner) is needed to perform impedance tuning of the load (plasma). Such impedance matching unit is known to use a slug tuner that has a plurality of slugs (see, e.g., Japanese Patent Application Publication No. 2003-347808).
The slug tuner includes a coaxial microwave transmission line formed of an outer conductor and an inner conductor provided within the outer conductor; a slug, formed of at least two dielectric bodies, provided in the gap, between the inside of the outer conductor and the outside of the inner conductor, which can freely move along a longitudinal direction of the inner conductor; and a driving unit for moving these slugs to perform impedance tuning. Thus, a compact and low loss tuner can be realized.
However, in such a microwave plasma source, if a microwave power applied is increased, the temperature of an antenna and/or a microwave transmitting plate rises due to the heat transferred from the plasma and the heat caused by microwave loss. These heats may have an undesirable impact on the mobility of the slugs in a slug tuner.